The effects of the nutritional state, muscular activity, substrates, hormones and hormone deficiencies, particularly diabetes mellitus, on amino acid metabolism, will be investigated in rats. The effect of some of the above factors, particularly that of the branched chain amino acids (bcaa) on protein turnover in muscles and the regulation of the branched chain amino acids (bcaa) on protein turnover in muscles and the regulation of the branched chain x-keto acid (bcka) dehydrogenase system at the cellular level will be studied. The latter system is rate limiting for bcaa catabolism in several tissues includng muscles. We previously reported that 1) bcaa oxidation by muscles is stimulated in protein catabolic states, e.g., fasting and diabetes, 2) bcaa, particularly leucine, play a regulatory role in muscle protein turnover which entails stimulation of protein synthesis and inhibition of proteolysis. The former effect appears to involve peptide chain initiation, is synergistic with that of insulin and may be required for the anabolic effect of insulin after a prolonged fast. The mechanism of the diabetes induced stimulation of bcaa oxidation will be studied in isolated muscles and cell free muscle preparations. Questions to be asked include the following: What is the role of substrates and hormones (e.g., thyroid hormone, glucocorticoids, glucagon, GH)? Is the oxidation of the three bcaa affected in parallel? Does accelerated bcaa oxidation always accompany accelerated protein catabolism in muscle? Is the former a cause or an effect of the latter? Is the bcaa dehydrogenase system present in an active and an inactive form in muscle mitochondria? The effect of bcaa, insulin and the nutritional state and the interaction of these factors in the regulation of protein synthesis and degradation, the turnover of rRNA and peptide chain initiation will be studied in vivo in rat muscles. The latter will be investigated by studies of ribosomal profiles, measurement of ribosomal subunit content and assay of an eIF-2 like initiation factor in muscle. Finally, preliminary data suggest that the release of some amino acids, e.g., basic amino acids and tryptophan from muscles may be regulated at the transport step; in vitro studies with isolated muscles from control & diabetic rats.